The present invention is directed to bicycles and, more particularly, to a bicycle twist-grip shift control device that uses parallel gearing to communicate rotational power from a twist-grip to a transmission control element.
Twist-grip shift control devices have been used with bicycles to pull and release transmission control elements in response to rotation of a twist-grip operating member that rotates coaxially with a handlebar axis. An example of such a device is shown in U.S. Pat. No. 5,315,891. The device disclosed in that patent includes a twist-grip operating member that rotates coaxially around a handlebar axis, a drive gear that rotates coaxially with the operating member, a driven gear that meshes with the drive gear and rotates around an axis that is parallel to the handlebar axis, and a cable reel that rotates coaxially with the driven gear for winding and unwinding a transmission control cable. The operating member rotates in clockwise and counterclockwise directions from a home position to correspondingly rotate the cable reel. A retainer mechanism maintains the cable reel in the selected position so that the operating member may return to the home position after each operation.